The present invention relates to a purge device for an automotive steering system and a method of purging trapped gases therefrom.
Hydraulic power assisted steering systems are known and have been widely used in the automotive industry. A typical steering gear housing includes a steering piston chamber and a rack moveably disposed in the chamber. The housing further includes a piston with two sides disposed on the rack and placed in the chamber between two hydraulic assist ports formed on the chamber. Each side faces one of the ports. Typically, pressurized hydraulic fluid, e.g., power steering fluid, is added to one side of the piston and drained from the other side of the piston via fluid lines in fluid communication with the ports. In some steering gear housings, the location of the ports relative to the top of the chamber permits gases, such as air, of lower density relative to the hydraulic fluid to undesirably accumulate at the top of the chamber portion during installation and operation of the steering system. Trapped air therein significantly degrades the dynamic performance of the hydraulic power assisted steering system principally due to its high compressibility relative to the hydraulic fluid in the system.
The present invention generally provides a device and method for purging trapped gas from a piston chamber of a vehicle hydraulic steering system. A purge channel which extends from a hydraulic assist port formed on the chamber is disposed in the piston chamber. The purge channel, through which power steering fluid flows, has an opening disposed at a top portion of the chamber in which air or fluid of lower density relative to the power steering fluid becomes trapped during installation and operation of the steering gear assembly. The channel is in fluid communication with the top portion of the chamber. During installation of the steering system, gases such as air may become trapped therein as hydraulic fluid is initially introduced into the system. Moreover, during operation of the steering system, the channel receives air in the top portion of the chamber. Then, air is purged or vented therefrom and through the purge channel to facilitate the dynamic performance of the hydraulic steering system. This prevents the accumulation of air trapped in the top portion of the chamber.